Evaluation of Quality Changes in Walnut Kernels (Juglans regia L.) by Vis/NIR Spectroscopy

Abstract

Storage of walnut kernels in light and at room temperature, as is common practice, is detrimental to their sensory quality and shelf life. This study demonstrates that Vis/NIR spectroscopy, in combination with multivariate data analysis (chemometrics), is a most capable rapid method for monitoring the overall quality deterioration of walnut kernels. Spectral predictions of the sensory attributes nutty and rancid tastes by partial least-squares regression (PLSR) resulted in correlations (r²) of 0.77 and 0.86, respectively, whereas with PLSR prediction of the chemical parameter hexanal content a correlation (r²) of 0.72 was obtained. The study further establishes that storage in light results in pronounced oxidative changes, especially in walnuts stored at 21 °C, whereas dark storage at 5 °C results in walnuts without any trace of rancid taste during 25 weeks of storage at accelerated storage conditions (50% oxygen). Keywords: Walnuts (Juglans regia L.); sensory evaluation; lipid oxidation; light; temperature; NIR; Vis; PCA; PLSR